Flag register

Flag register:-It contains 5 single bit flags and three unused bits which changes its status according to the result stored in an accumulator. It is also known as status registers.

        There are five flip-flops in the flag register are as follows:

                                1.Sign flag(S)

                                2.zero flag(z)

                                3.Auxiliary carry flag(AC)

                                4.Parity flag(P)

                                5.Carry flag(C)

Bit position of flags in flag register

1.Sign (S)- If D7 of the result is 1 then sign flag is set otherwise reset. As we know that a number on the D7 always decides the sign of the number.

if D7 is 1: the number is negative.

if D7 is 0: the number is positive.

2.Zero (Z)-If the result stored in an accumulator is zero then this flip flop is set otherwise it is reset.

3.Auxiliary carry(AC)-If any carry goes from D3 to D4 in the output then it is set otherwise it is reset.

4.Parity (P)- If the no of 1's is even in the output stored in the accumulator then it is set otherwise it is reset for the odd.

5.Carry Flag (CY)- If the result stored in an accumulator generates a carry in its final output then it is set otherwise it is reset.